One of the most difficult tasks of search and rescue (SAR) operations are marine rescue operations at night times and heavy weather. Locating a person swimming in the open ocean from larger distances is nearly impossible. Even when a rescue team, independently if situated on a vessel or in an air-bound rescue vehicle, is very close to the swimmer, the swimmer itself is hard to discover. This is caused by obstacles such as e.g. the ocean waves, rain, fog, and darkness. Ocean waves have mostly heights exceeding the height of the swimmer over the water surface by multiple times. Land-based rescue operations, such as alpine rescue operations are another example of such difficult tasks.
Therefore, various types of signalling devices for signalling the position of persons in an emergency or for locating equipment have been proposed in the past.
For instance a warning and signalling system including a kite attached to a flexible rope is disclosed in U.S. Pat. No. 4,768,739. The kite is used as an enhanced visibility warning and signalling device. The kite is carried aloft by blowing wind. However, a kite 12 always needs at least a certain amount of relative air movement, such as wind, in order to keep the kite at a certain height. This is illustrated in FIGS. 1C and 1D. To keep the signalling device at a minimum height is essential for the efficiency of detecting persons in emergency. In situations of very calm weather or windless weather conditions, a kite will drop to the surface and not fulfill the signalling purpose. Moreover, a kite is sensitive to turbulence and gets easily unstable, which leads to the kite crashing down on the surface. This is a basic disadvantage of kites, limiting the range of use unnecessarily. Furthermore, for injured or handicapped persons it is not possible to launch a kite.
Therefore location and signalling balloon devices have been proposed, e.g. in U.S. Pat. No. 4,944,242. A balloon body is in case of an emergency situation filled with a lighter-than-air gas from e.g. a pressurised container or a chemical reaction. The inflated balloon is fixed to a tether line, which is e.g. attached to the person in emergency or to the ground near that person, in order to signal the position of that person to search and rescue (SAR) operations. However, balloons have a number of disadvantages when being used as signalling devices. Balloons are not suitable for use in windy weather conditions in contrast to the above mentioned kites. With increasing wind velocity a balloon 1, fixed to a surface below by means of a tether line, will be drawn down to the surface due to the resulting force FT on the balloon being dominated by the dragging force FD of the wind on the balloon. This is illustrated in FIGS. 1A and 1B. The inclination angle α decreases from no wind (vw=0) with increasing wind vw>0. One possibility to solve this problem is to increase the size of the balloon being filled with gas. However, this option is very limited for the use in emergency signalling kits. This is due to the fact that these kits should be as compact and lightweight as possible when not in use. This condition limits both the size of such a balloon and the amount of available gas for inflating the balloon.
In order to overcome the drawbacks of signalling devices being based on purely a kite or a balloon, it has been proposed to aerodynamically shape balloons in the form of a kite, e.g. in the patent application CA-A-2172852, or in the form of a wing, e.g. in U.S. Pat. No. 4,815,677. U.S. Pat. No. 3,657,752 discloses a locator device for locating submerged equipment having returned to the surface of an ocean. The device generates gas by a chemical reaction of a compound with water, whereupon the gas inflates a balloon-kite flying aloft tethered to a container at sea level. The balloon-kite is radar-detectable and ascends into the air above the water by means of the buoyancy of the gas-filled part of the balloon-kite and/or the aerodynamic lift of the kite part of the balloon-kite. This is illustrated in FIGS. 1E and 1F. However, also these devices combining a kite or a wing with a balloon have certain undesired drawbacks. For example it is desired that a dragging force that is exerted by the signalling device on the tether line is generally constant at the point where it is fixed to a person in emergency, a piece of equipment, or a ground surface. The dragging force should be constant within a certain limit. This ensures on the one-hand that the above-mentioned dragging force of the signalling device does not exceed a maximum load of the tether line, thus preventing its rupture. A rupture of the tether line which would render the signalling device useless as the kite or the balloon flowing away will no longer signal the desired location. In addition, a dragging force that comes close to or exceeds the weight of the equipment or person, whose position is to be signalled, will result in an undesired effect of moving the person or equipment. This may be a health hazard for e.g. a person drawn through the water, causing the person to unintentionally get water into the respiratory system. Moreover, in case of e.g. a child or non-heavy equipment, the signalling balloon may draw the child or the equipment over the ground, when used on land, resulting in injuries of the child or in damage of the equipment. In the worst case, the person or equipment will be raised out of the water or over ground. If the dragging force on the other hand becomes too low, the signalling device will not ascend sufficiently high and cannot fulfill its signalling purpose.
A kite-balloon or a wing-balloon has the advantage that it remains aloft properly under windless or low wind conditions due to the lifting force of the lighter-than-air gas in the balloon. Moreover, at high wind conditions, the aerodynamic shape of the kite or the wing compensates for the downward force imposed on the signalling device. At high wind conditions, even these devices, not withstanding the problem of tether-line-rupture, will become unstable due to turbulent behaviour of the kite or wing as mentioned above.
Thus, there is a need for a new signalling device based on a combination of a wing or kite with a balloon, avoiding the above-identified problems and ensuring a generally constant dragging force on the tether line.